Large scale commercial production of continuous glass fibers (E-glass and C-glass types) comprises melting batch materials consisting primarily of minerals that are crystalline or substantially crystalline in nature. Conversion of these crystalline raw materials to a glassy state requires significant energy to be applied during the melting process. In view of the significant energy investment accompanying crystalline materials, glassy or amorphous minerals have sometimes been used in the production of glass compositions. A glassy or amorphous structure can reduce the amount of energy consumed in the melting process. Glassy minerals such as basalt and obsidian, for example, have been used as significant portions of feedstock for the production of mineral wool.
An associated disadvantage with some glassy minerals, however, is the high iron content of such minerals. Basalt and obsidian both comprise relatively large amounts of iron, thereby making their resulting melts highly energy absorbing. As a result, use of conventional gas fired furnaces is typically impractical for melt processing of these minerals. Electrical melting can be used to process glassy minerals of high iron content, but this is often a constraint in high volume glass fiber production as compared with conventional gas fired furnace technology. Raw materials used in the production of E-glass and C-glass fibers are generally low in iron, thereby permitting the use of large scale gas fired furnaces.
Perlite (and its expanded form pumice) is a mineral that naturally occurs in the glassy form. Perlite has not been extensively used as a raw material in glass production, partially because of its compositional parameters. The major constituents of perlite are SiO2, Al2O3 and alkali oxide (R2O). SiO2 is typically present in perlite in an amount between about 70 and about 75 weight percent. Al2O3 is typically present in perlite in an amount between about 12 and about 15 weight percent. Alkali oxides are typically present in perlite in an amount between about 3 and about 9 weight percent. These parameters conflict with the compositional requirements of several widely used glass compositions, including, for example, those of E-glass and C-glass.
E-glass compositions, for example, are well-suited for forming glass fibers. As a result, the majority of glass fibers used in reinforcement applications, such as polymeric reinforcement applications, are formed from E-glass compositions. E-glass compositions generally limit the amount alkali oxides to no more than 2 percent. The high alkali oxide content of perlite is inconsistent with this limitation and renders perlite largely unsuitable for use in batch compositions for the production of E-glass compositions.
Moreover, C-glass compositions have also been used to form fibers resistant to corrosion in acidic environments. In order to resist acidic corrosion, C-glass compositions comprise a high SiO2 content and a low Al2O3 content (<8 wt. %). The high Al2O3 content of perlite generally precludes use of perlite in batch compositions for the production of C-glass compositions.